Iron‐ and Cobalt‐Catalyzed Asymmetric Hydrosilylation of Ketones and Enones with Bis(oxazolinylphenyl)amine Ligands

Abstract

Chiral bis(oxazolinylphenyl)amines proved to be efficient auxiliary ligands for iron and cobalt catalysts with high activity for asymmetric hydrosilylation of ketones and asymmetric conjugate hydrosilylation of enones.

Asymmetric Reduction of Electron-Rich Ketones with Tethered Ru(II)/TsDPEN Catalysts Using Formic Acid/Triethylamine or Aqueous Sodium Formate

“…25 (2H, d, J 8.7 Hz), 6.92 (2H, d, J 8.7 Hz), 4.83 (1H, q, J 6.5 Hz), 3.18−3.14 (4H, m), 1.76−1.70 (4H, m), 1.60− 1.52 (2H, m), 1.48 (3H, d, J 6.5 Hz); δ C (100 MHz, CDCl 3 ) 151. 8, 136.3, 126.3, 116.4, 70.1, 50.7, 25.8, 24.7, 24.3 20 [α] D 25 45.9 (c 1.0 in CHCl 3 ) 93% ee (R)); ν max 3343, 2832, 1609, 1514, 1449, 1262, 1208, 1118, 1090, 1062, 920, 818, 624, 560, 446 cm −1 ; δ H (400 MHz, CDCl 3 ) 7.30 (2H, d, J 8.7 Hz), 6.88 (2H, d, J 8.7 Hz), 4.82 (1H, q, J 6.5 Hz), 3.82 (4H, t, J 5.0 Hz), 3.12 (4H, m), 1.80 (1H, br s), 1.45 (3H, t, J 6.5 Hz); δ C (100 MHz, CDCl 3 ) 150. 8, 137.3, 126.4, 115.7, 70.0, 66.9, 49.4, 24.9; m/z (ESI) 230.0 ([M + Na] + ), 208.1 ([M + H] + ).…”

New Chemistry with Anionic NNN Pincer Ligands

“…The asymmetric hydrosilylation of ketones using metal-BPI (M¼Fe, Co) and Fe (OAc) 2 /BOPA catalytic systems is an effective method for the synthesis of chiral alcohols following hydrolysis (Scheme 21) [37,38,[102][103][104]. While the use of BPI-Co and BPI-Fe complexes resulted in hydride transfer to the Si-face to give the R-alcohol, the stereochemistry of the product with BOPA ligands was dependent upon the presence (or absence) of zinc powder.…”

Title Pages

“…Extending the theme of transition metal catalysis, applications of lowcost and 'friendly' iron is now a familiar theme and diverse in nature. Recently reported are, among others, an asymmetric transfer-hydrogenation of aryl ketones with a chiral iron(II) bis(isonitrile) complex 26 ; an iron-(or cobalt)-catalyzed asymmetric hydrosilylation of ketones with chiral bis(oxazoline) complexes 27 ; regioselective 1,2-hydrosilylation of 1,3-dienes with iron bis-(2-pyridylaldimine) complexes 28 ; an iron-catalyzed dehalogenation of aryl halides 29 ; and inexpensive routes to key N-heterocyclics (including indoles) via iron-catalyzed cyclodenitrogenation of azides 30 . Catalysis with osmium is less diverse, but it is worth mentioning, perhaps, the elusive 7-endo-cycloisomerization to 1,2-dihydro-3-benzoxepines which is far more efficient than under Ru-, Rh-or W-catalysis 31 ; note also the osmium equivalent of Noyori′s homogeneous asymmetric hydrogenation of ketones 32 , affording high enantioselectivities with astonishing TOF values up to 300,000 h -1 .…”